Land managers wishing to monitor the groundwater on their property have recognized the advantages of being able to divide a single borehole into a number of zones to allow monitoring of groundwater in each of those zones. If each zone is sealed from an adjacent zone, an accurate picture of the groundwater can be obtained at many levels without having to drill a number of boreholes that each have a different depth. A groundwater monitoring system capable of dividing a single borehole into a number of zones is disclosed in U.S. Pat. No. 4,204,426 (hereinafter the '426 patent). The monitoring system disclosed in the '426 patent is constructed of a plurality of casings that may be connected together in a casing assembly and inserted into a well or borehole. Some of the casings may be surrounded by a packer element made of a suitably elastic or stretchable material. The packer element may be inflated with fluid (gas or liquid) or other material to fill the annular void between the casing and the inner surface of the borehole. In this manner, a borehole can be selectively divided into a number of different zones by appropriate placement of the packers at different locations in the casing assembly. Inflating each packer isolates zones in the borehole between adjacent packers.
The casings in a casing assembly may be connected with a variety of different types of couplers or the casing segments may be joined together without couplings. One type of coupler that allows measurement of the quality of the liquid or gas in a particular zone is a coupler containing a valve measurement port (hereinafter the measurement port coupler). The valve can be opened from the inside of the coupler, allowing liquid or gas to be sampled from the zone surrounding the casing.
To perform sampling, a special measuring instrument or sample-taking probe is provided that can be moved up and down within the interior of the casing assembly. The probe may be lowered within the casing assembly on a cable to a known point near a measurement port coupler. As disclosed in the '426 patent, when the probe nears the location of the measurement port coupler, a location arm contained within the probe is extended. The location arm is caught by one of two helical shoulders that extend around the interior wall of the measurement port coupler. As the probe is lowered, the location arm slides down one of the helical shoulders, rotating the sample-taking probe as the probe is lowered. At the bottom of the helical shoulder, the location arm reaches a stop that halts the downward movement and circumferential rotation of the probe. When the location arm stops the probe, the probe is in an orientation such that a port on the probe is directly adjacent and aligned with the measurement port contained in the measurement port coupler.
When the probe is adjacent the measurement port, a shoe is extended from the side of the sample-taking probe to push the probe in a lateral direction within the casing. As the shoe is fully extended, the port in the probe is brought into contact with the measurement port in the measurement port coupler. At the same time the probe is being pushed against the measurement port, the valve within the measurement port is being opened. The probe may therefore sample the gas or liquid contained in the zone located outside of the measurement port coupler. Depending upon the particular instruments contained within the probe, the probe may measure different characteristics of the exterior liquid or gas in the zone being monitored, such as the pressure, temperature, or chemical composition. Alternatively, the probe may also allow samples of gas or liquid from the zone immediately outside the casing to be stored and returned to the surface for analysis or pumped to the surface.
After the sampling is complete, the location arm and the shoe lever of the probe may be withdrawn, and the probe retrieved from the casing assembly. The valve in the measurement port closes when the shoe of the probe is withdrawn, thus separating the gas or liquid in the zone outside the measurement port from the gas or liquid inside. It will be appreciated that the probe may be raised and lowered to a variety of different zones within the casing assembly, in order to take samples at each of the zones. A land manager may select the type of probe and the number and location of the zones within a borehole to configure a groundwater monitoring system for a particular application. The expandability, and flexibility of the disclosed groundwater monitoring system therefore offers a tremendous advantage over prior art methods requiring the drilling of multiple sampling wells.
While the measurement port coupler shown in the '426 patent allows multilevel sampling and monitoring within a borehole, it requires that the underground fluid samples be removed from a particular underground zone and transported within the probe to the surface where fluid analysis takes place. Offsite analysis suffers from many drawbacks. First, it is labor intensive. The fluid sample must be removed from the probe, transported elsewhere, and subsequently tested. Additionally, each step required by this offsite testing increases the probability of both quantitative and qualitative testing errors. Furthermore, removing the underground fluid sample from its native environment invariably compromises the accuracy of the offsite tests due to changes in, for example, pressure, pH, and other factors that cannot be controlled in sample transport and offsite testing. Finally, removal of a fluid sample from the contained fluid within a particular zone can compromise the physical characteristics of the remaining fluid within that zone such that the accuracy of future testing is affected. Fluid pressure can be compromised to the extent that minute rock fissures close, prohibiting or greatly increasing the difficulty of the gathering of future fluid samples.
A need thus exists for an in situ underground sample analyzing apparatus having a probe suitable for lowering into the ground to a specific zone level for extracting and analyzing fluid samples in situ. The present invention is directed to fulfilling this need. This need is particularly evident where the permeability or natural yield of fluid from the geologic formations is very low and/or where the natural environment is readily disturbed by conventional sampling methods.